The present invention refers to an Hydraulic Pumping Unit, for the use in oilwells, characterized by the use of an kinetic energy accumulation system, to compensate the upward and downward moving masses of the rod strings.
The Hydraulic Pumping Units are often used in oilwells because they present operational advantages as compared with the conventional mechanical pumping unit. The even and straight movement of the hydraulic piston can be transmitted immediately to the string of sucker rods, without the use of gears and transmission belts. Because of the small weight of the Hydraulic Pumping Unit, the same can be mounted directly on the wellhead flange, avoiding in this way the need for the heavy bases necessary with mechanical pumping units. Stroke length and speed can be easily adjusted without the loss of time to change belt pulleys, and the absence of gear reducers, roller bearings and belt-drives helps to reduce the cost of maintenance, It must be mentioned also, that the initial cost of the Hydraulic Pumping Unit is normally much smaller than that of an mechanical unit.
In spite of the advantages mentioned above, and the apparent simplicity of the Hydraulic Pumping Unit in its actual configuration, the same presents some operational problems which are the causes of frequent failures of operation and increased cost of maintenance.
In the first place, the problem of balancing of the moving masses, which is solved at the mechanical unit with simple rotating counterweights, must be mentioned.
Almost all of the Hydraulic Pumping Units actually in operation, use one of the following systems for balancing:
1 Use of hydraulic accumulators with floating piston or with an elastic bladder, both of them with pre-charge of high pressure nitrogen. This system presents the inconvenience to need frequent recalibration of the nitrogen pressure. Also, the floating piston gets easily stuck, due to the small pressure differential between oil and nitrogen, and the lifetime of the elastic bladder is not long enough to be satisfactory for the conditions at oilfields. PA0 2 Different configurations of pulleys, cables or chains, moving mechanically guided carriers for counterweights, are also used for balancing of Hydraulic Pumping Units, but the introductions of all these elements increase considerably the cost of maintenance.
With the intention to solve the inconveniences mentioned above, the present invention was developed in accordance with the disposition shown in the annexed drawings and the following detailed description.